Atrial fibrillation (Afib) is a condition in which the normal beating of the left atrium (LA) is chaotic and ineffective. The left atrial appendage (LAA) is a blind pouch off the LA. In patients with Afib blood stagnates in the LAA facilitating clot formation. These clots (or clot fragments) have a tendency to embolize or leave the LAA and enter the systemic circulation. A stroke occurs when clot/clot fragment embolizes and occludes one of the arteries perfusing the brain. Anticoagulants, e.g. Coumadin, have been shown to significantly reduce the stroke risk in Afib patients. These drugs reduce clot formation but also increased bleeding complications including hemorrhagic strokes, subdural hematoma and bleeding in the gastrointestinal tract.
There are about 8 million people in the US and EU with Afib. About 4.6 million of these patients are at a high risk for stroke and would benefit from anticoagulation. A large portion of these patients cannot take anticoagulants due to an increased bleeding risk leaving their stroke risk unaddressed. The prevalence of Afib increases with age.
Several devices for occluding the LAA are described in the prior art and each has limitations this invention improves upon. The prior art devices are metal structures which are circular in cross section and are made to expand to fill the LAA ostium. These devices are offered in many sizes and must be closely matched to the highly variable LAA anatomy. This is difficult to do using fluoroscopy and often requires adjunctive imaging in the form of transesophageal echocardiography, cardiac CT and MRI, all with three dimensional reconstructions. If the device is significantly oversized, the LAA ostium may become overstretched leading to tearing resulting in bleeding into the pericardial space. If the device is too small, it will not adequately seal the ostium and may be prone to embolization. Even if sized correctly, the device forces the oval LAA ostium to take the round shape of the device, often resulting in residual leakage at the edges due to poor sealing.
Anchoring of these implants in the proper location is described in the prior art devices predominately using an array of radially disposed barbs or hooks which engage into the surrounding cardiac tissue upon expansion of the device. The device must therefore have sufficient spring force or stiffness for the barbs to engage the surrounding tissue. These barbs may lead to leaking of blood through the tissue into the pericardial space which may lead to cardiac tamponade. Furthermore, the geometry of these barbs and hooks prevent additional positioning once the implant is fully expanded.
For all of these reasons it would be desirable to have a device which did not require an excessive number of sizes requiring extensive pre-procedure imaging, could be repositioned when fully expanded and secured without an array of hooks or barbs.